The present invention relates to a semiconductor acceleration sensor having such functional elements including an acceleration sensor chip and signal-processing chip sealed in a resin molding package, and to a method of manufacturing such a semiconductor acceleration sensor.
Airbag systems, antilock brake systems (ABS), and navigation systems are exemplary of the increasingly common automotive systems that rely on a semiconductor acceleration sensor to detect vehicle acceleration and impact. A semiconductor acceleration sensor typically comprises an acceleration sensor chip and a signal-processing chip in a package that both protects the internal chips from the external environment and determines the outside shape of the sensor unit. In many conventional systems, these packages are protected by a metal cover. As these systems have been adapted for smaller, lower priced vehicles, demand for compact, low cost systems has led to the adoption of systems in which the components are sealed in a molded resin package.
FIG. 6 is a section view of a resin sealed semiconductor acceleration sensor according to the related art. In this conventional semiconductor acceleration sensor 50, the acceleration sensor chip 53 is fixed to the die pad 61 by a die bond resin 63. The signal-processing chip 55 is mounted on the acceleration sensor chip 53, and is electrically connected via metal wires 59a to acceleration sensor chip 53. A plurality of outer leads 57 is disposed around the chips 53 and 55 with each outer lead 57 electrically connected to the signal-processing chip 55 via a metal wire 59b. The components are then secured in their specified positions and protected from the outside environment by resin molding 52, leaving only the outside parts of the outer leads 57 exposed.
The acceleration sensor chip typically detects acceleration or impact by detecting the minute displacement of a mass. As a result, it is preferably not exposed to external stresses other than that being detected. An acceleration sensor chip sealed in a resin molding as described above, however, is subject to stress produced by the expansion or contraction of the resin package resulting from changes in the temperature of the external environment. The offset and output sensitivity of the acceleration sensor depend on the temperature characteristics of the sensor and can vary greatly when this external stress exceeds a particular level, thereby making it difficult to assure good acceleration and impact detection precision.
To avoid this problem and absorb and alleviate stress from the resin molding 52 acting on the acceleration sensor chip 53, a damping member 54 made of rubber or other resilient material is typically provided around the outside surfaces of the acceleration sensor chip 53 in this conventional semiconductor acceleration sensor 50. In this example according to the related art, the damping member 54 is fixed to the outside circumference surface of the acceleration sensor chip 53 by way of die bond resin 63.
As described above, a damping member 54 surrounding the outside of the acceleration sensor chip 53 is used in this conventional semiconductor acceleration sensor 50 to absorb and buffer stress on the acceleration sensor chip 53 from the resin molding 52, and is sealed together with the acceleration sensor chip 53 and signal-processing chip 55 in the resin package. As will be understood from FIG. 7, however, the package resin 52 may displace the die bond resin between the damping member 54 and acceleration sensor chip 53 during the packaging process. When this happens, thermal expansion and contraction of resin 52a between the damping member 54 and acceleration sensor chip 53 will directly stress the acceleration sensor chip 53.